DCS, DSA, and SA are three different sets of caps which have different designs.
DSA has a flat, spherical shape, and every row of keys is the same height. Spherical means that the four sides are high, and the center is concave.
SA is also spherical, though it's considered "sculpted" (I think that's the right word), meaning each row has a different height and angle, such as you would imagine from a normal keyboard. They are also a bit taller than your average caps. Generally, they go like this: Row 1 is the top two rows (F row and number row), row 2 is QWER, row 3 is ASDF, and row 4 are the bottom two rows. Some sets of SA caps (like for an ErgoDox) are preferred to have all row 3 in SA such that the keys can be interchanged based on the user's desired layout.
DCS is cylindrical. This means the left and right side are high, and the entire center portion is concave. This is the most common type of cap we see today (at least when it comes to mechanical keyboards). The row system applies here as well. If you're looking for something for one of the top two rows, then you would choose Row 1.
http://www.keycapsdirect.com/key-caps.phpHopefully this helps you while you look at this link.
